The market for metal containers has developed widely in recent years due in part to the introduction of the easy open end. While the easy opening feature has been shown to be both effective and convenient, it has given rise to a collateral problem of littering, since traditionally the easy opening feature was pulled free from the container to expose the contents and then subsequently discarded. The indiscriminate disposal of the pull tabs is not only unsightly, but can also present a safety hazard particularly on beaches and in parks. Further, the relatively small size of the separated tab presents a challenge to those concerned with the collection and recycling of waste material. The solution to this problem resides in a nondetachable tab and preferably a tab which is compatible with the end closure and is recyclable.
While the industry has addressed this problem by developing a number of closure structures, one of the more successful has been a can end which employs a retained lever tab. In this structure, the tab is joined to the container end by a tongue or flap which is lanced in the web of the tab and which serves as a hinge or connecting strip. Typically, the tip of the tongue is apertured and staked to end by means of an integral rivet. Typically, tab rigidity is provided by utilizing heavy aluminum tab stock and by curling the edges of the stock to form a tab. Since the tab functions by levering open a scored portion of the end panel it must be sufficiently rigid to prevent distortion of its curled rim when leverage is applied to the lift end of the tab to effect rupture and displacement of the scored panel. At the same time, the tongue of the tab must be sufficiently bendable to permit the user to open the container and subsequently bend the tab back out of the way into a position of repose.
The basic end is formed in a high speed inverted stamping press and same is converted to a tabbed end with a integrally formed rivet. U.S. Pat. No. 4,026,226 is the inverted press wherein the end is formed in the lower section of the press and the tab is formed in the upper section of the press above the crown. The two are assembled in the last stage of the progressive operation in the lower section of the press by staking the integrally formed rivet in the central panel of the end so as to secure the tab tongue to the end. This combination is then transferred to a belt which includes pockets for holding the formed and tabbed ends in a horizontal position with the tab exposed upwardly. These ends are tested with pressure transduced by acoustics to determine whether or not there is a leak in the end, e.g., about the score or about the rivet. Once this is done, the ends are ready to be fed to the machine for bagging for shipment or for double seaming to the filled containers. Frequently an end is applied to a container which has no tab for reasons related to the high speed nature of the operation and the fully automated manufacturing process. This situation is unacceptable because the double seam used for such ends is not easily used with a can opener and the convenience of the built in opening tab is not available. It therefore became important to detect whether or not there was a tab applied to the end as well as whether or not the end had a pressure leak. This invention relates to the equipment used to make that determination in an efficient high speed manner by detecting which end can be used and which must be rejected because there is no tab.
Accordingly, it is a primary objective of the instant invention to provide a method and transducer for monitoring an easy open end with a structure sufficiently accurate and simple as to effectively determine whether or not there is a tab or multiple ends are stacked in the feed belt pockets.
It is a further object of this invention to provide a novel fixture and transducer combination which can readily detect multiple ends, missing ends or missing tabs prior to a double seaming operation to secure the end to a filled closure or before bagging the ends for shipment.